Glycerol is a trihydric alcohol, 1,2,3-propanetriol, and has been known to mankind since the late 18th century. Since its discovery from fats and oils it has been used in a number of applications, which extend to the thousands. The major current uses of glycerol include food, cosmetics, pharmaceuticals, plastics, toothpaste, urethane foam, explosives, synthetic resins, ester gums and other miscellaneous applications.
One process of producing glycerol has water and fat fed into a splitting column under pressure (up to 6 Mpa) and above 220° C. leading to a 15% solution of crude glycerol and fatty acid. This crude glycerol is further purified and distilled to make it into a pharmaceutical grade. The glycerol that results from fat splitting is a natural glycerol and if the oil used is of vegetable origin, it could be of kosher grade.
The major user of fatty acids from fat splitting is the soaps and detergents industry. Therefore, the glycerol production varies depending upon the soap demand.
Glycerol is also manufactured from various streams of petroleum products like glycidol and epichlorohydrin. Petroleum derived glycerol is a synthetic glycerol and is declining in volume. Glycerol production from fermentation is another emerging technology but currently has limited scope.
Major derivatives of glycerol include esters, acetals, ethers and amines. Alkyd resins use glycerol and phthalic anhydride. Various partial glycerol fatty acid esters are used as food emulsifiers in large quantities.
One of the major derivatives of glycerol is polyglycerols. Polyglycerols are ether oligomers produced by self-condensation of glycerol. Polyglycerols and their derivatives are extensively used in industrial, food and cosmetic applications. For example, polyglycerol esters function as emulsifiers, dispersants, spreading agents, flavor or fragrance carriers, rheology modifiers, solubilizers and emollients.
One type of commercial production process of polyglycerol employs alkaline condensation of glycerol. One of the important members of polyglycerols is diglycerol. Other commercial production processes are more directed condensation process by reacting glycerol with epichlorohydrin, followed by hydrolysis, neutralization and purification. These other processes lead to a higher purity diglycerol. Desirable diglycerol properties include solubility in water and aqueous systems, compatibility with electrolytes, biocompatibility as it is recognized by skin components for various cosmetics applications, high hydrogen bonding propensity, imparting humectant properties to the product, high hydroxyl value which acts as a crosslinking agent in a variety of applications including the formation of gels, no reactivity with the active components of the formulation and environmental compatibility, as it readily biodegrades.
The worldwide production of glycerol is currently about 900 thousand tons/year. Roughly 20% of this volume is produced in United States. Most of the glycerol, about 90%, is produced from fats and oils from fat/oil splitting during fatty acid production. In the last decade, due to the improved worldwide economy, the demand for soaps increased thereby increasing fat splitting and glycerol production.
Additionally, in the past two decades the developmental efforts to use fats and oils and their by products for other industrial applications has increased considerably. This is partially driven by the “green” image perceived by the public and the environmental benefits associated with the use of renewable raw materials.
Biodiesel fuel is an alternative product that has been developed and is supported by the recent higher prices of petroleum-based products and the desire to reduce the dependency on foreign petroleum. The benefits of environmentally acceptable products include lower pollution (air, water and soil), and minimal health and safety risks. Also, there are some legislative incentives and requirements that are prodding industries to move towards less polluting and environmentally friendly products. In spite of all these drivers, the use of industrial products is primarily dictated by cost and performance.
Biodiesel fuel is produced by transesterification of fat/oil with methanol. Typically a base catalyst is used to facilitate the transesterification. A typical mass balance of this reaction—about 100 lbs of vegetable oil will react with about 10 lbs of methanol and a fraction of a lb of sodium methoxide (catalyst) to yield about 100 lbs of biodiesel fuel and 10 lbs of glycerol. However, the yields and quality of the output depends upon the feedstock.
Increased biodiesel fuel production worldwide has dampened the prices of glycerol. It is theorized that in the United States alone if the production of biodiesel fuel reaches a billion gallons/year, it will increase the glycerol production by 200%. This increased glycerol production volume will glut the market and likely drop the prices to less than half of the current level.
Therefore, a need exists for using the glycerol from increased production to benefit industry. Additionally, using glycerol based products will be economically advantageous based on the large supply of glycerol and potentially low cost of glycerol.